1. Field of the Invention
The invention concerns a drive for separating the engine from the vehicle wheels upon a torque reversal condition and more particularly, to means for reengaging the engine and wheels in response to brake actuation and a heated brake condition.
2. Description of the Prior Art
Overrunning devices for separating the engine and wheels upon certain torque conditions have been employed in vehicles. As used herein, the term overrunning device refers to not only a clutch which transmits torques coming from the engine as also from the vehicle (during engine braking), but also a true overrunning device which connects the engine with the wheels only at torques coming from said engine and separates it on torque reversal. Torque reversal occurs not only during automotive operation and when the accelerator pedal is moved into its idling position but in general also when the number of revolutions of the output shaft of the engine drive unit becomes smaller than the number of revolutions of the wheel-side part of the overrunning device.
Automatic disengagement of the clutch when the accelerator pedal is in its idling position is known from U.S. Pat. No. 3,698,525 to Grassmuck. In the event that the braking action of the engine during overrunning should be required, the vehicle operator can reengage the clutch by actuation of a switch. For example, German DE No. 28 03 145 A1 describes a type of overrun disconnection apparatus wherein supply of an operating quantity (ignition current, fuel) to the internal combustion engine is interrupted when the accelerator pedal is in its idling position and the engine speed is above the idling speed. German patent application Nos. P 29 45 304.1-21 and P30 13 878.4 (corresponding to U.S. Ser. No. 350,525 filed Apr. 2, 1981) contain proposals for disconnecting the internal combustion engine during the idling phases and the restarting phase thereof as a function of the prevailing engine speed, either directly through the kinetic energy of the vehicle after engagement of the clutch, or through the electric starter motor.
These constructions and arrangements facilitate a fuel-saving manner of driving coupled with a simple operation of the internal combustion engine. However, disengagement of the overrunning device (i.e. clutch), and a possible stopping of the engine implies an attendant loss in the braking effect of the engine, resulting in an additional load on the brake, particularly during extended downhill driving. Therefore, control of an overrunning or clutch disengagement device should not be left solely to the discretion of the vehicle operator.